The present invention relates to the use of foamable compositions for packaging purposes. In a number of packaging applications, fragile articles or those which otherwise need to be protected from movement or breakage, particularly items with irregular shapes and sizes, have been packed in protective foamed polymer packaging materials, such as injection molded styrofoam, styrofoam chips, or other similar materials.
One particular technique for packaging articles in foam comprises of methods in which the foam is generated in place during the process of packaging the articles. For example, when certain chemicals are mixed together they form polymeric products while at the same time they generate gases such as carbon dioxide and water vapor. If those chemicals are selected so that they harden following the generation of the carbon dioxide and water vapor, they can be used to form hardened polymer foams in which the mechanical foaming action is caused by the gaseous carbon dioxide and water vapor leaving the mixture.
One technique for foam in place packaging is to place the object to be packaged in a container, cover it with a polymer film or other material which will protect it from liquids, inject a certain amount of a foamable composition into the remainder of the container, and then close the container. As the composition foams, it fills the remainder of the container, forming a custom shaped foam cushion surrounding the article.
More recently, machines have been developed for 5 automatically providing the foam cushioning. For example, in U.S. Pat. No. 4,674,268 to Gavronsky et al., which is assigned to the assignee of the present invention, an apparatus is disclosed which forms plastic bags from plastic tubing and inserts a predetermined amount of a foamable composition into the bags while leaving ventilation openings in the bag. As the foamable composition foams and generates gases, they escape through the ventilation openings while the bag fills with foam. In a particular application, the bag can be placed into a container for packaging purposes immediately after the foamable composition has been added. When the container is closed, the foam within the bag expands to occupy a large proportion, and often all, of the remaining container space surrounding the article or articles in the container. The plastic bag protects the articles from the foam and the result is an efficient customized packaging system. The contents of U.S. Pat. No. 4,674,268 are hereby incorporated by reference.
A similar apparatus which forms such bags from plastic sheet material is described in U.S. Pat. No. 121,223 filed Nov. 16, 1987 on behalf of Charles R. Sperry and Ser. No. 07/236,013, filed Aug. 22, 1988, on behalf of Pinarer et al, and both also assigned to the assignee of the present invention. The contents of both of these applications are hereby incorporated by reference.
One problem with the foamable compositions, however, is that some of the more useful polymers which they form tend to have somewhat adhesive properties. As a result, the foamable composition, which is often dispensed as a somewhat viscous liquid, tends to stick to objects that it strikes and harden into foam. One location where this causes a particular problem is the injection nozzle or cartridge from which the foam is ejected. As those familiar with such foamable compositions are aware, the compositions are often formed from two precursors. These precursors must be withheld from mixing with one another until just prior to
injection so that a typical injection cartridge or nozzle contains the means for allowing the two foam precursors to enter the cartridge, mix with one another, and then exit therefrom as the foamable composition. Accordingly, as an injection nozzle operates over and over again, particularly in automated or successive fashion, foamable composition tends to build up around the injection opening, harden into foam, and block the proper exiting of further foamable composition. As a result, the injection nozzles either have to be manually cleaned, or mechanically wiped as in the Gavronsky description. The mechanical articulation required to mechanically wipe such nozzles tends to be rather complicated, and adds associated expense and potential for mechanical problems.
Where automated machines for repetitively producing plastic bags containing foamable composition are used, however, it is disadvantageous to have to continue to interrupt the packaging process to clean the injection nozzle, or to correct the operation of a complicated mechanical wiping system. Nevertheless, no satisfactory method has been developed for repeatedly and automatically cleaning the foamable composition from such injection nozzles and keeping them clean as foam is repetitively injected through them, while avoiding the mechanical complexity of an automated wiping system.
Therefore, it is an object of the present invention to provide a self-cleaning injection nozzle which includes means for automatically cleaning foamable composition from the nozzle, particularly the opening portion, on a repetitive basis, using a minimum of moving parts.